It is known in the art to fabricate glazing units by laminating a ply of polyvinyl butyral ("PVB") or other flexible polymeric laminating material to a coated glass substrate ply. The coating frequently is carried on an inner surface of the glass substrate ply, that is, a surface which forms a laminated interface with the PVB. Metal-based interfacial coatings are used, for example, in electrically heated glazing units, such as electrically heated motor vehicle windshields, and in automotive and architectural glazing units which provide solar load reduction, that is, selective transparency to visible light. The interfacial coatings used for such purposes typically comprise a transparent, electrically conductive film or film stack deposited onto the inner surface of the glass ply. An exemplary such film stack may comprise, for example, at least one film of silver or other metal sandwiched between (or alternating with) films of zinc oxide or other dielectric material. Other films, such as adhesion films, etc. may also be included in the film stack.
Interfacial coatings in a laminated glazing unit may interfere with interfacial adhesion. Metal-based coatings, for example, may be susceptible to corrosion. Glazing units having electrically conductive, transparent film stacks at a laminated interface have been known to experience corrosion after prolonged exposure to certain environmental conditions. Specifically, such corrosion may occur at the peripheral edge of the glazing unit where the edge of the coating is exposed. The corrosion of the coating may, over time, extend progressively into the interface from the edge of the glazing unit. Ultimately, the corrosion may adversely affect the performance of the coating.
Those skilled in the art are aware of certain methods for improving the lamination between a coated substrate and a laminating material such as PVB. In U.S. Pat. No. 4,650,557 to Bitter there is teaching directed to a process for making a curved, coated glass member suitable for use, for example, in architectural glass, heated mirrors and heated windows, such as electrically heated windshields. A process disclosed in the Bitter patent for producing a laminated glazing unit having a coated interfacial surface includes a step wherein a peripheral zone mask is silk-screened onto a substrate ply. The substrate surface with the peripheral zone mask thereon is then sputter coated with an electrically conductive film stack. The silk-screened mask is then removed, leaving an uncoated peripheral zone. The purpose disclosed in the Bitter patent for such uncoated peripheral zone is to prevent the conductive film stack from being accidentally grounded to any contiguous conductive material. The silk-screened mask is removed by oxidation when the sputter coated substrate ply is fired to oxidize the sputtered film. Bitter suggests that a separate step for oxidation of the sputtered film would be unnecessary if the substrate were heated during the sputter coating operation, but that in such case some other, unspecified means for removing the silk-screened mask would have to be employed.
It is an object of the present invention to provide a laminated glazing unit having an interfacial coating, which glazing unit is more environmentally durable. More specifically, it is an object of at least certain preferred embodiments of the invention to provide a method of making a laminated glazing unit which is less susceptible to progressive edge corrosion resulting from prolonged exposure to environmental conditions. Additional objects and features of the present invention will be better understood in view of the following disclosure.